Permselective membranes suitable for use in desalination of aqueous solutions are the subject of numerous patents. Cadotte U.S. Pat. No. 4,277,344 discloses perselective multi-layer membranes in which there is a microporous polysulfone substrate layer and a juxtaposed polyamide layer made from an aromatic triacid halide and an aromatic diamine. Scala et al. U.S. Pat. No. 3,744,642 discloses multilayer membranes in which one layer is a porous substrate and the juxtaposed layer is a polyamide, a polyphenylester, or a polysulfonamide. Hara et al. U.S. Pat. No. 4,353,802 discloses semipermeable composite membranes in which the membrane material is cross-linked using polyfunctional aromatic acid halides. Kamiyama et al. U.S. Pat. No. 4,619,767 discloses permselective multi-layer membranes having a (1) microporous substrate layer (2) an ultra thin layer of a cross-linked polyvinyl alcohol/amino compound and (3) a porous inner layer of water insoluble polyvinyl alcohol located between the porous substrate and ultra thin layer. Other patents disclosing the preparation and properties of thin film composites are U.S. Pat. Nos. 3,951,815; 4,005,012; 4,039,440 and 4,277,344.
Thin film composite (TFC) membranes appear to be the most efficient reverse osmosis (R.O.) membranes known today. These membranes are conveniently made by interfacial condensation polymerization to yield ultra thin films at the interface of an aqueous phase layer and a non-aqueous or organic (solvent) phase layer. Since the two phases are substantially immiscible, a super thin film will be generated at the interface of the two layers. Since the reaction is diffusion controlled and self-limiting, the method yields ultra thin films, typically 50-5000 .ANG. thick.